Acupuncture and electroacupuncture have been increasingly adopted in North America as a complement to pharmacotherapy for chronic pain over the last twenty years (1997 NIH Consensus Statement on Acupuncture). At least thirty years of research indicate a role for opioidergic systems in the mechanisms underlying acupuncture-evoked analgesia. However, the mechanism(s) underlying the effectiveness of acupuncture for pain management remains only partially understood. In recent years a role for NMDA receptor antagonists to enhance opioid analgesia by inhibition of the development of analgesic tolerance has been clearly defined. However, the contribution of endogenous modulators of the NMDA receptor system to analgesia induced by acupuncture has been minimally explored. Agmatine (decarboxylated arginine) is an endogenous substance that antagonizes the NMDA receptor and inhibits nitric oxide synthase. Like synthetic NMDA receptor antagonists, agmatine also inhibits development of opioid tolerance and dependence. Since agmatine is expressed in the CNS, strategies could be used to optimize its activity in CNS regions where electroacupuncture exerts therapeutic benefit. The objective of this application is to determine the mechanism by which agmatine contributes to electroacupuncture-evoked analgesia. The central hypothesis is that endogenous agmatine exerts its effects through inhibition of the NMDA receptor at the NR2B receptor subunit. The rationale for the proposed research is that, with demonstration of endogenous agmatine participation in electroacupuncture-evoked analgesia and identification of the mechanism, endogenous agmatine could be regulated in site-specifically to optimize electroacupuncture therapy. Two specific aims are proposed: #1: Determine the extent to which and the mechanism by which endogenous agmatine contributes to electroacupuncture-induced pain control. #2: Determine the ability of electroacupuncture to release endogenous agmatine. This contribution will be significant because understanding how agmatine manifests its effects is an important step toward optimizing its therapeutic application in both non-pharmacological and pharmacological pain management approaches. The research proposed in this application is innovative because it represents a new mechanism to explain analgesia evoked by electroacupuncture, a commonly applied non-pharmacological pain management therapy that is not well understood. The successful completion of this research is expected to position both electroacupuncture and agmatine as complementary approaches to improve pain management and therapy that may translate to other therapeutic indications arising from maladaptive neuroplasticity.